Dispersion-based adhesives based on polyvinyl esters find multifarious application, as for example in the adhesive bonding of paper or cardboard packaging for producing folding boxes, envelopes, brochures, or cigarettes. Products of this kind are customarily manufactured industrially by production line fabrication. The dispersion-based adhesives in such applications are applied to the substrate generally by machine application methods such as nozzle application systems or roll technologies. With these application methods, instances of adhesive-related fouling, caused by imprecise or uncontrolled application of adhesive, also referred to as “splashing”, lead to fabrication problems. If adhesive gets onto the conveyor belt, there may be instances of sticking of the fabricated material, resulting in machine downtime and inconvenient cleaning work. Nozzle application is frequently accompanied by conical deposits at the nozzle exit point, diverting the jet of adhesive emerging from the nozzle. This is detrimental to precise control of adhesive application and can also lead to contamination and, ultimately, to the shutdown of the unit. In nozzle application systems, the dispersion-based adhesives are supplied by pumps through line systems to a nozzle having a rapidly opening and closing valve, with switching frequencies of up to 1000/second, for example. Nozzle valve cycle frequencies of such levels subject the dispersion-based adhesives inside the nozzle to extremely high shearing forces. Suitable dispersion-based adhesives are required accordingly to have very high shear stability.
The application of dispersion-based adhesives by machine methods is described for example in EP-A 1889890 or in EP-A 1887018. The polyvinyl esters used for such application have been prepared by emulsion polymerization according to batch or semibatch processes. There continues nevertheless to be a need for dispersion-based adhesives which even better meet the requirements of machine application methods.